Microdata DOM API - Web APIs
itemvalue [ = value ] returns the element's value.
... each element that adds a property also has an itemvalue idl attribute that returns its value.
... var user = document.getitems('http://example.net/user')[0]; alert('hello ' + user.properties['name'][0].itemvalue + '!'); the htmlpropertiescollection object, when indexed by name in this way, actually returns a propertynodelist object with all the matching properties.
... the getvalues method the propertynodelist object must return a newly constructed array whose values are the values obtained from the itemvalue idl attribute of each of the elements represented by the object, in tree order.

HTMLElement - Web APIs
htmlelement.itemref read only returns a domsettabletokenlist… htmlelement.itemprop read only returns a domsettabletokenlist… htmlelement.itemvalue returns a object representing the item value.
... living standard added the following properties: translate, itemscope, itemtype, itemid, itemref, itemprop, properties, and itemvalue.